In the swash-plate type compressor, a swash-plate is rigidly secured obliquely to a rotary shaft or is secured obliquely to a rotary shaft in such a manner that its slanting angle is variable. The compression and expansion are carried out by means of the swash-plate which increases or decreases the volume of a partition space within a compressor, depending upon the rotation of the rotary shaft. Such swash plate is caused to slide on a sliding member referred to as a shoe. Air-tight mutual sealing is attained between parts, so that the cooling medium can be compressed and expanded in the stated space.
A noticeable point in the sliding conditions of a swash-plate is that, during the initial operational period of a compressor, the cooling medium reaches the sliding part prior to the lubricating oil reaching the sliding part between the swash plate and the shoe; thus the cooling medium has a rinsing effect on the lubricating oil which remains on the sliding part, with the result that the sliding condition is in a dry condition free of lubricating oil. The sliding condition requirements of the swash plate are therefore very severe.
The sliding properties, which are required for a swash-plate used under the condition described above, are seizure resistance, wear resistance, and the like. Proposals have thus been made to add hard matters into the aluminum material for enhancing the wear resistance, to improve the material of the swash plate, and to subject an iron-based swash-plate to heat treatment for enhancing the hardness and hence wear-resistance.
In addition, the following surface treating methods are also proposed.
One of the present applicants proposed in Japanese Unexamined Patent Publication No. Sho 51-36611 to bond sintered Cu material on the shoe in the case of an iron-based swash plate. That is, an iron-based swash plate was heretofore subjected to hardening treatment. However, when the material of the opposed member, i.e., the shoe, is an iron-based material, the sliding takes place between identical kinds of materials thereby involving a problem that a seizure is liable to occur. Sintered copper alloy is used for the opposing material (shoe) opposed to an iron-base swash plate, so as to avoid the above mentioned problem.
In addition, it was also proposed to apply tin plating on the iron-based swash-plate so as to avoid the sliding between identical kinds of materials and hence to enhance the seizure resistance.
Since the tin plating applied on an iron-based swash-plate is soft, a problem that arises is insufficient wear-resistance. Furthermore, although a hard element added to an aluminum alloy enhances wear resistance, a problem that arises is insufficient seizure resistance.
It is therefore an object of the present invention to enhance the performance and reliability of a swash-plate type compressor by means of providing on the surface of an iron-based or aluminum-based swash plate a surface layer which exhibits improved both seizure resistance and wear resistance.